My ancestry is from Romania, Poland, Ukraine, and Belarus. I haven't been able to track back into Eastern Europe except for Poland, where a relative hired a professional genealogist who managed to go back to the 1700s. I have no way to verify that information is accurate. On the Romanian branch, I have third cousins who only immigrated to the US as adults and we were able to piece together some bits from photos and postcards that were passed down.
At some point, I'd like to figure out the provenance of my surname (Soffian). Typically names ending in "ian" are Armenian, but I'm fairly confident the Soffian branch of my ancestry is from Ukraine. (Armenia never had much of a Jewish population so it would be unlikely.)
I have a friend who tracked his ancestry into English royalty. He's got a tree with over 10,000 names on it.
[1]: A "Kuckuckskind" (German for "cuckoo's child") is a child who's social father is not their biological father. However, this is unkown to both the child and the father, only the mother knows this. I didn't find prove if this is an actual english analogy, so... here you go.